The invention relates to a method for operating an internal combustion engine with a fuel supply device for at least a first and a second fuel, wherein the internal combustion engine includes at least one cylinder which has at least one intake valve and to which air, in particular fresh air, can be supplied via an intake pipe. The invention further relates to an internal combustion engine.
Methods of the afore-stated type are known in the art. The internal combustion engine includes the cylinder which is provided with the at least one intake valve. Connected to the intake valve on the side facing away from the cylinder is the intake pipe via which air can be supplied to the intake valve and thus also to the cylinder. The air is preferably fresh air or includes at least a proportion of fresh air. In principle, the air may also include at least a proportion of exhaust gas that results from an exhaust gas recirculation. Furthermore, the internal combustion engine includes the fuel supply device by which fuel can be fed into the cylinder for subsequent combustion.
Basically, it can be differentiated between direct injection and manifold injection. In direct injection, fuel is supplied directly into the cylinder or a combustion chamber of the cylinder. Conversely, in manifold injection, fuel is first supplied to the intake pipe from which it enters together with air through the intake valve into the cylinder or its combustion chamber. Direct injection thus represents a direct fuel supply and manifold injection an indirect fuel supply into the cylinder or the combustion chamber. In direct injection, only air is preferably supplied to the cylinder; formation of a mixture of air and fuel takes place directly in the combustion chamber. Direct injection enables in particular an operation in the presence of excess air so that a reduction in fuel consumption can be realized. In manifold injection on the other hand, the mixture formation of air and fuel occurs already in the intake pipe, resulting in the formation of a very homogenous mixture.
The internal combustion engine introduced here is designed for operation with different fuels, that is at least the first fuel and the second fuel which differs from the first fuel. For example, the first fuel is a gaseous fuel and the second fuel is a liquid fuel. Operation of the internal combustion engine with gaseous fuel has the advantage that a CO2 emission reduction by about 25% can be realized. Internal combustion engines designed for operation with liquid fuel are normally adapted to suit the operation with gaseous fuel. As the different fuels normally exhibit very different properties, significant advantages can be realized, when the internal combustion engine is suited to only one of the fuels.
For example, gaseous fuel exhibits a very high anti-knock property so that fuel consumption can be significantly reduced, when the internal combustion engine is suited to only gaseous fuel. However, as the internal combustion engine should be able to operate with both fuels, it is necessary to adapt the internal combustion engine to all intended fuels. The totality of fuels contemplated for the operation thus determines the configuration of the internal combustion engine. Accordingly, the higher anti-knock property of the gaseous fuel cannot be exploited because the liquid fuel usually exhibits a substantially lower anti-knock property.